Side-by-side dual gun crt having horizontal deflector plates provided with side shields for correction of geometric distortion

ABSTRACT

A cathode ray tube having dual electron beam guns and associated deflection means is described in which the electron beam guns are disposed in a plane containing the tube axis and such that the electron beam guns are located in planes spaced to the left and right of the tube axis which are normal to the first mentioned plane so that the electron beam guns are parallel to provide asymmetrical horizontal scanning thereby requiring less space in the tube neck. The horizontal deflection plate means is provided with side shields which provides dynamic geometry correction as the tube is operated.

States atent [191 SIDE-BY-SIDE DUAL GUN CRT HAVING HORIZONTAL DEFLECTOR PLATES PROVIDED WITH SIDE SHIELDS FOR CORRECTION OF GEOMETRIC DISTORTION Kenneth William Hawken, Newberg, Oreg.

Inventor:

Assignee:

Filed:

Appl. No.:

Tektronix, lnc., Beaverton, Oreg.

Feb. 12, 1973 References Cited UNITED STATES PATENTS 8/1956 Haeff 315/13 CG 3,670,199 6/1972 Hawes 315/13 R Primary Examiner-T. H. Tubbesing Assistant Examiner,l. M. Potenza Attorney, Agent, or Firm-Adrian J. La Rue [57] ABSTRACT A cathode ray tube having dual electron beam guns and associated deflection means is described in which the electron beam guns are disposed in a plane containing the tube axis and such that the electron beam guns are located in planes spaced to the left and right of the tube axis which are normal to the first mentioned plane so that the electron beam guns are parallel to provide asymmetrical horizontal scanning thereby requiring less space in the tube neck. The horizontal deflection plate means is provided with side shields which provides dynamic geometry correction as the tube is operated.

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VERT AMP has Fig-4C Fig4B Fig-4A SIDE-BY-SIDE DUAL GUN CRT HAVING HORIZONTAL DEFLECTOR PLATES PROVIDED WITH SIDE SHIELDS FOR CORRECTION OF GEOIVETRIC DISTORTION BACKGROUND OF THE INVENTION The present invention relates generally to electron beam tubes having dual beams and associated deflection means, and more particularly to cathode ray tubes having dual electron beam guns that provide asymmetrical horizontal scanning and side shield means are provided by the horizontal deflection plate means to provide dynamic geometry correction during operation of the tube.

Cathode ray tubes having dual electron beam guns are known wherein stacked electron guns are disposed above and below the tube axis in a plane passing therethrough so that the horizontal angle of sweep of the electron beams are swept across the tube target equiangularly on each side of the tube or gun axis. In order for each gun to scan to same area of target, the guns are angled, but such angling distorts the scanned pattern from a rectangle to a trapezoid. With stacked guns, this trapezoidal distortion is easily corrected by adjusting the horizontal deflectors to be nonparallel from side to side thereby affecting the horizontal sensitivity as the tube is scanned vertically. If a divergent post deflection accelleration (PDA) field is used and full overlap of scan is desired, the guns have to be angled quite steeply thereby resulting in a larger diameter CRT which takes up useful space.

SUMMARY OF THE INVENTION The present invention reduces CRT volume in the gun area by disposing the electron beam guns side-byside and parallel to each other and in a plane containing the tube axis and the use of side shield means by the deflection plates for the horizontal scan in order to correct for trapezoidal distortion.

An object of the present invention is to provide a dual beam CRT in which parallel electron beam guns are disposed side-by-side to render the gun area smaller.

Another object of the present invention is the provision of a dual beam CRT wherein the horizontal deflection means is provided with dynamic geometry correction means.

A further object of the present invention is to provide a dual beam CRT in which the dynamic geometry correction means comprises side shield means to prevent trapezoidal distortion.

An additional object of the present invention is the provision of a dual beam CRT having two pairs of horizontal deflection plates in which side shield plate means extend inwardly from the outer plates and cover the gap between respective pairs of the plates.

A still further object of the present invention is to provide an improved cathode ray tube having two electron beam deflection means in which trapezoidal distortion is eliminated from the beam displays in a simple and inexpensive manner.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of this invention will become apparent from the following detailed description of an illustrative embodiment which is to be read in conjunction with the accompanying drawing in which:

FIG. I is a schematic diagram of the cathode ray tube of the present invention;

FIG. 2 is a horizontal sectional view taken along the line 2-2 of FIG. 1 formed of the deflection means;

FIG. 3 is a view taken along the line 3-3 of FIG. 1;

and I FIGS. 4A, 4B and 4C illustrate rectangular displays formed by an electron beam on the fluorescent screen of a cathode ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, a cathode ray tube 10 or other electron beam deflection device has an evacuated envelope 12 of glass, ceramic or other suitable insulating material in which a fluorescent screen 14 of phosphor material coated on the inner surface of a light transparent faceplate 16 which is secured onto the front end of such envelope. A thin metallic coating 17 preferably of aluminum is disposed on the gun side of screen 14.

Two separate electron guns of conventional design are disposed in envelope 12 which include cathodes 18 and 20, control grids 22 and 24 and focusing anodes 26 and 28. In addition, two separate electron beam deflection systems are provided in envelope 12 including a first pair of vertical deflection plates 30 and a second pair of vertical deflection plates 32 as well as a first pair of horizontal deflection plates 34 and a second pair of horizontal deflection plates 36. Thus, cathode 18 has associated therewith control grid 22, focusing anodes 26, vertical deflection plates 30 and horizontal deflection plates 34 for controlling the electron beam 18a emanating from cathode 18 whereas cathode 20 has associated therewith control grid 24, focusing anodes 28, vertical deflection plates 32 and horizontal deflection plates 36 for controlling the electron beam 20a emitted from cathode 20. Cathodes l8 and 20 operate at 3KV.

Horizontal deflection plates 34 and 36 are identical in configuration and each pair comprises an outer planar plate 38 and an inner plate 40 which has a rear section disposed at a slight angle away from its electron beam axis and a forward section disposed at a greater angle away from its electron beam axis. Thus, the horizontal deflector plates are usually essentially flat plates facing each other and bent to form a wedge-shaped spacing between them. Side shields 42 are provided by outer plates 38 which cover the gap between plates 38 and 40 at least along forward sections of plates 40. Side shields 42 can be integral extensions of plates 38 or additional metallic members secured as by welding onto plates 38. Side shields 42 may also extend from plates 40, and they may have an angular edge, when they are part of plates 38, which coincides with the angular disposition of the forward section of plates 40. Alternatively, side shields 42 may be independent plates disposed in position adjacent plates 38 and 40 via dielectric mounting means in a conventional manner.

An inner gun shield 44 is disposed between the pairs of horizontal deflection plates 34 and 36 in order to prevent the electrostatic fields generated by the respective pairs of horizontal deflection plates from affecting each other. Shield 44 is operated at near the average potential of the potential of the horizontal deflection means.

Compensator plates 46 are mounted between the pairs of vertical deflection plates to prevent the electrostatic fields of these vertical deflection means from interfering with each other as well as providing compensation so that the characteristic impedance is constant therealong. Plates 46 are operated at near the average potential of the vertical deflection means.

isolation shield 48 is disposed between the output ends of the vertical deflection plates 30 and 32 and the imput ends of the horizontal deflection plates 34 and 36 and it includes vertical slots 50 and 52 through which the electron beams 18a and 20a pass. Shield 48 isolates the electrostatic fields of the vertical deflection means from the electrostatic fields of the horizontal deflection means and it is operated at near the average potential of the vertical and horizontal deflection means.

An annular mounting and shielding member 54 is disposed in envelope 12 so that it has the output ends of horizontal deflection means 34 and 36 positioned therein and it is operated at near ground potential. Member 54 serves to shield the horizontal deflection means from the high voltage of post deflection acceleration 56 which consists of a conductive coating on the interior surface of envelope 12 in electrical contact with metallic coating 17 and has an operating voltage of ZOKV thereon. A scan expansion mesh 58 is secured on the member 54 which has an outwardly-directed hemispherical configuration to provide diverging lens for scan expansion and it causes the electron beams to be effectively scanned over the screen in full overlap operation.

lnput signals are applied at input terminals 60 and 62 which are connected respectively to vertical amplifiers 64 and 66. The outputs from vertical amplifiers 64 and 66 are connected respectively to vertical deflection means 30 and 32. Horizontal ramp generators 68 and 70 are triggered in response to the receipt of input signals at input terminals 60 and 62 by providing trigger circuits 72 and 74 having their inputs connected respectively to input terminals 60 and 62 and having their outputs connected respectively to the inputs of horizontal ramp generators 68 and 70 which in turn have their outputs connected respectively to horizontal deflection means 34 and 36.

Thus, electron beams 18a and 20a emitted respectively from cathodes l8 and 20 are properly focused by focusing anodes 26 and 28, thereafter vertical deflection means 30 and 32 and horizontal deflection means 34 and 36 operate on the focused electron beams to deflect the beams in accordance with the signals at input terminals 60 and 62 whereafter the beams are passed through scan expansion mesh 58 whereby they are accelerated about 2lKV before they strike the target comprising phosphor layer 14 and metallic coating 17 which produces light images of these electron beams, which under most circumstances, will be the signal waveform traces of the vertical deflection signals. The thin film of aluminum, which is several angstroms thick, is electron transparent and reflects the light emitted by the phosphor layer 16 to increase the brightness of the displays in a conventional manner.

As can be discerned, the electron guns and their associated deflection means are disposed side by side instead of in a conventional stacked condition so that the axes of these dual electron guns and associated deflection means are located in a plane containing tube axis TA. Thus, the axis of the electron guns are disposed equidistantly on each side of tube axis TA. The parallel disposition of the electron guns enables the neck of the CRT to be smaller so that more room is provided in an instrument in which the CRT is disposed. The left electron beam 18a is scanned a small angle to the left when viewing the screen and a large angle to the right over the entire screen, whereas the right electron beam 200 is scanned a large angle to the left and a small angle to the right over the entire screen. Thus, the electron beams can simultaneously scan over the entire screen in an overlapping manner thereby displaying dual images thereon for observation.

In the absence of side shields 42 for the horizontal deflection means 34 and 36, the display generated by the left electron gun means would provide a trapezoidal display as shown in FIG. 4A whereby the horizontal lines above and below the center horizontal line will de viate away therefrom in a direction from left to right, whereas the display generated by the right electron gun means would provide a trapezoidal display as shown in FIG. 4B whereby the horizontal lines above and below the center horizontal line will deviate away therefrom in a direction opposite to that of the display of the left gun means as shown by FIG. 4A. Thus, the interaction of the electrostatic fields of the vertical and horizontal deflection means without side shields 42 for the horizontal deflection means will provide displays having trapezoidal distortion as shown by FIGS. 4A and 4B in a dual beam CRT wherein the electron guns are disposed parallel. When side shields 42 are provided for the horizontal deflection means in accordance with the present invention, a true rectangular display as shown in FIG. 4C is provided thereby correcting for trapezoidal distortion. As the electron beams are scanned horizontally by the horizontal deflection means, they receive some vertical delfection by the action on the electrostatic field established by the side shields and this is the necessary direction for correction of the trapezoidal distortion.

The invention relative to the provision of side shield means for the horizontal deflection means can also be used in the case of a storage CRT wherein the electron gun and associated deflection means are offset relative to the tube axis and the flood gun axis is coincident with the tube axis so that only a single flood gun is used, and in its axis being coincident with the tube axis, the flood gun electrons are uniformly distributed over the screen.

The vertical deflection means, as hereinabove described, can be used in a CRT which will operate up to megahertz, however, for CRT operation above this bandwidth, the vertical deflection means will be of the type disclosed in US. Pat. No. 3,694,689.

Thus, there has been described a CRT in which dual electron gun means are disposed parallel and side-byside to reduce neck size of the CRT and the horizontal deflection means is provided with side shield means to correct for trapezoid distortion.

It will be obvious to those having ordinary skill in the art that many changes may be made in the details of the above-described preferred embodiment without departing from the spirit of the invention. For example, rather than two cathodes, a single cathode may be employed to produce both electron beams transmitted through the two deflection means. Also, while a conventional CRT has been described, it is also possible to employ the present invention in a bistable charge image storage tube including the type in which the phosphor layer also functions as the storage dielectric. Therefore, the scope of the present invention is to be determined by the following claims.

The invention is claimed in accordance with the following:

I. An electron beam apparatus comprising:

an evacuated envelope having target means;

dual electron gun means disposed side-by-side in said envelope on each side of a central axis of said envelope and spaced from said target means for generating electron beams therefrom; and

deflection means for each of said dual electron gun means disposed between said electron gun means and said target means for deflecting said electron beams over said target means in accordance with signal voltages applied thereto to provide image displays thereover.

2. An electron beam apparatus according to claim 1 wherein said dual electron gun means are parallel to each other.

3. An electron beam apparatus according to claim 1 wherein said deflection means are disposed to deflect said electron beams over said target means in simultaneous overlapping relationship.

4. An electron beam apparatus according to claim 1 wherein said deflection means comprise vertical deflection means and horizontal deflection means with the vertical and horizontal deflection means for one of said dual electron gun means deflecting the electron beam thereof a small angle and then a large angle during a horizontal scanning operation thereof and with the vertical and horizontal deflection means for the other of said dual electron gun means deflecting the electron beam thereof a large angle and then a small angle during a horizontal scanning operation thereof.

5. An electron beam apparatus according to claim 1 wherein means are provided by said deflection means to correct for trapezoidal deflection of said electron beams.

6. An electron beam apparatus according to claim 5 wherein said means provided by said deflection means comprise side shield means for horizontal deflection means thereof.

7. An electron beam apparatus according to claim 6 wherein said side shield means is integrally connected to one of the horizontal plates of said horizontal deflection means.

8. A cathode ray tube comprising:

an evacuated envelope having target means;

electron gun means disposed in said envelope for generating electron beam means and being spaced from said target means;

deflection means disposed in said envelope between said target means and said electron gun means and including vertical and horizontal deflection plate means for deflecting said electron beam means over said target means in accordance with signal voltages applied to said vertical and horizontal deflection plate means; and

side shield means provided by said horizontal deflection plate means for correction of trapezoidal distortion of said electron beam means.

9. A cathode ray tube according to claim 8 wherein said electron gun means comprise dual electron gun means disposed side-by-side in said envelope.

10. A cathode ray tube according to claim 8 wherein said side shield means are integrally connected to said horizontal deflection plate means.

11. A cathode ray tube according to claim 8 wherein said electron gun means comprise dual electron gun means and said deflection means comprise independent vertical and horizontal deflection means for each of said dual electron gun means.

12. A horizontal deflection system for an electron beam apparatus comprising:

spaced plate means having rear sections and forward sections; and

side shield means disposed at right angles relative to at least said forward sections and covering the gap therebetween.

13. A horizontal deflection system according to claim 12 wherein said side shield means are integrally connected to one of said plate means.

14. A horizontal deflection system according to claim 12 wherein said plate means comprise pairs of spaced plate means disposed in alignment and said side shield means are integrally connected to outer plate members which extend toward each other.

7 Disclaimer 3,819,984.Kemwth William H awlcen, Newberg, Oreg. SIDE-BY-SIDE DUAL GUN CRT HAVING HORIZONTAL DEFLEOTOR PLATES PROVIDED'VVITH SIDE SHIELDS FOR CORREC- TION OF GEOMETRIO DISTORTION. Patent dated June 25, 1974. Disclaimer filed Nov. 19, 1975, by the assignee, Telatwom'w, Ina. Hereby enters this disclaimer to all claims of said. patent.

[Oyfioz'al Gazette March 9, 1.976.]

Disclaimer 3,819,984L.Ke0meth W illiam Hawlcen, Newberg, Oi'eg. SIDE-BY-SIDE DUAL GUN CRT HAVING HORIZONTAL DEFLECTOR PLATES PROVIDED 1TH SIDE SHIELDS FOR CORREC- TION OF GEOMETRIC DISTORTION. Patent dated June 25, 1974. Disclaimer filed Nov. 19, 1975, by the assignee, Teict rom'm, low. Hereby enters this disclaimer to all claims of said patent,

[Ofiicial Gazette Mamh .9, 1.976.] 

1. An electron beam apparatus comprising: an evacuated envelope having target means; dual electron gun means disposed side-by-side in said envelope on each side of a central axis of said envelope and spaced from said target means for generating electron beams therefrom; and deflection means for each of said dual electron gun means disposed between said electron gun means and said target means for deflecting said electron beams over said target means in accordance with signal voltages applied thereto to provide image displays thereover.
 2. An electron beam apparatus according to claim 1 wherein said dual electron gun means are parallel to each other.
 3. An electron beam apparatus according to claim 1 wherein said deflection means are disposed to deflect said electron beams over said target means in simultaneous overlapping relationship.
 4. An electron beam apparatus according to claim 1 wherein said deflection means comprise vertical deflection means and horizontal deflection means with the vertical and horizontal deflection means for one of said dual electron gun means deflecting the electron beam thereof a small angle and then a large angle during a horizontal scanning operation thereof and with the vertical and horizontal deflection means for the other of said dual electron gun meaNs deflecting the electron beam thereof a large angle and then a small angle during a horizontal scanning operation thereof.
 5. An electron beam apparatus according to claim 1 wherein means are provided by said deflection means to correct for trapezoidal deflection of said electron beams.
 6. An electron beam apparatus according to claim 5 wherein said means provided by said deflection means comprise side shield means for horizontal deflection means thereof.
 7. An electron beam apparatus according to claim 6 wherein said side shield means is integrally connected to one of the horizontal plates of said horizontal deflection means.
 8. A cathode ray tube comprising: an evacuated envelope having target means; electron gun means disposed in said envelope for generating electron beam means and being spaced from said target means; deflection means disposed in said envelope between said target means and said electron gun means and including vertical and horizontal deflection plate means for deflecting said electron beam means over said target means in accordance with signal voltages applied to said vertical and horizontal deflection plate means; and side shield means provided by said horizontal deflection plate means for correction of trapezoidal distortion of said electron beam means.
 9. A cathode ray tube according to claim 8 wherein said electron gun means comprise dual electron gun means disposed side-by-side in said envelope.
 10. A cathode ray tube according to claim 8 wherein said side shield means are integrally connected to said horizontal deflection plate means.
 11. A cathode ray tube according to claim 8 wherein said electron gun means comprise dual electron gun means and said deflection means comprise independent vertical and horizontal deflection means for each of said dual electron gun means.
 12. A horizontal deflection system for an electron beam apparatus comprising: spaced plate means having rear sections and forward sections; and side shield means disposed at right angles relative to at least said forward sections and covering the gap therebetween.
 13. A horizontal deflection system according to claim 12 wherein said side shield means are integrally connected to one of said plate means.
 14. A horizontal deflection system according to claim 12 wherein said plate means comprise pairs of spaced plate means disposed in alignment and said side shield means are integrally connected to outer plate members which extend toward each other. 